Wireless, optically-powered optoelectronic sensors

ABSTRACT

The technology disclosed in this patent document can be used to construct devices with opto-electronic circuitry for sensing and identification applications, to provide untethered devices for deployment in living objects and other applications, and to provide fabrication techniques for making such devices for commercial production. As illustrated by specific examples disclosed herein, the disclosed technology can be implemented to provide fabrication methods, substrates, and devices that enable wireless, inorganic cell-scaled sensor and identification systems that are optically-powered and optically-readout.

PRIORITY CLAIMS AND RELATED PATENT APPLICATIONS

This patent document claims the priorities and benefits of (1) U.S.Provisional Patent Application No. 62/628,190 entitled “WIRELESS,OPTICALLY-POWERED OPTOELECTRONIC SENSORS and filed on Feb. 8, 2018(Attorney Docket No. 078554-8084.US00), and (2) U.S. ProvisionalApplication No. 62/740,326 entitled “WIRELESS, OPTICALLY-POWEREDOPTOELECTRONIC SENSORS” and filed on Oct. 2, 2018 (Attorney Docket No.078554-8084.US01). The entirety of the above applications isincorporated by reference as part of the disclosure of this patentdocument.

TECHNICAL FIELD

This patent document relates to sensing technology and opto-electronicdevices, systems and applications.

BACKGROUND

Sensors for sensing chemical or biological substances can be designed invarious configurations. In some designs, sensors can include electrodesto be tethered to electronic devices or processors via conductivewiring. Such wiring may have undesired effects. For example, tetheredimplants for monitoring neural activities can cause residual motionbetween neurons and electrodes as the brain moves and accordingly maylimit the ability to measure from peripheral nerves in moving animals,especially in smaller organisms such as zebra fish or fruit flies.Un-tethered wireless sensors are desirable for those and otherapplications.

SUMMARY

The technology disclosed in this patent document can be implemented toconstruct devices with opto-electronic circuitry for sensing andidentification applications, to provide untethered devices fordeployment in living objects and other applications, and to providefabrication techniques for making such devices for commercialproduction. As illustrated by specific examples disclosed herein, thedisclosed technology can be implemented to provide fabrication methods,substrates, and devices that enable wireless, inorganic cell-scaledsystems that are optically powered and optically readout.

In one aspect, for example, the disclosed technology can be implementedto provide a device with opto-electronic circuitry to include asubstrate; a photovoltaic module engaged to the substrate and structuredto convert light into electricity; and a sensor module engaged to thesubstrate and coupled to receive power from the electricity generated bythe photovoltaic module, the sensor module structured to include asensing element that is responsive to a target substance to produce aresponse. The sensor module is further configured to generate, based onthe response from the sensing element, an electrical sensor signalindicative of a property of the target substance. This device includes alight-emitting module engaged to the substrate and coupled to receivepower from the electricity generated by the photovoltaic module and toreceive the electrical sensor signal from the sensor module. Thelight-emitting module is structured to produce output light that ismodulated to carry the electrical sensor signal to wirelessly andoptically transmit the electrical sensor signal out of the device.

In another aspect, for example, the disclosed technology can beimplemented to provide method for sensing a target subject. This methodincludes implanting a sensor on a target subject without having aphysical connection to the sensor; directing illumination light onto thesensor implanted on the target subject to cause a photovoltaic module inthe sensor generate electric power for operating the sensor so that thegenerated electric power powers (1) a sensor module which performs asensing operation on the target subject to generate an electrical sensorsignal indicative of a property of the target subject, and (2) alight-emitting module coupled to receive the electrical sensor signalfrom the sensor module and operable to produce output light that ismodulated to carry the electrical sensor signal; and using the outputlight to wirelessly and optically transmit the electrical sensor signalout of the device.

In another aspect, for example, the disclosed technology can beimplemented to provide a device with opto-electronic circuitry toinclude a substrate; a photovoltaic module engaged to the substrate andstructured to convert light into electricity; and an identificationmodule engaged to the substrate and coupled to receive power from theelectricity generated by the photovoltaic module, the identificationmodule configured to generate an electrical sensor signal indicative ofan identity. This device includes a light-emitting module engaged to thesubstrate and coupled to receive power from the electricity generated bythe photovoltaic module and to receive the electrical sensor signal fromthe identification module. The light-emitting module is structured toproduce output light that is modulated to carry the electrical sensorsignal to wirelessly and optically transmit the electricalidentification signal out of the device.

In yet another aspect, for example, the disclosed technology can beimplemented to provide a method for constructing a device withopto-electronic circuitry. This method includes forming a semiconductorrelease layer over a semiconductor substrate; fabricatingphotoelectronic semiconductor structures over the semiconductor releaselayer; forming a polymer layer over the fabricated photoelectronicsemiconductor structures over the semiconductor release layer to embedthe fabricated photoelectronic semiconductor structures in the formedpolymer layer; performing an etching process to remove the semiconductorrelease layer to isolate the polymer layer and the fabricatedphotoelectronic semiconductor structures that are embedded in thepolymer layer; and transferring the polymer layer and the fabricatedphotoelectronic semiconductor structures that are embedded in thepolymer layer to a new substrate.

In yet another aspect, for example, the disclosed technology can beimplemented to provide a device with opto-electronic circuitry thatincludes a substrate and a heterostructure module formed on thesubstrate to include patterned semiconductor layers to convert incidentlight at an incident optical wavelength into electricity and emitsoutput light an output optical wavelength different from the incidentoptical wavelength. A sensor module is engaged to the substrate andcoupled to receive power from the electricity generated by theheterostructure module, the sensor module structured to include asensing element that is responsive to a target substance to produce aresponse and the sensor module is further configured to generate, basedon the response from the sensing element, an electrical sensor signalindicative of a property of the target substance. This device furtherincludes circuitry coupled to the heterostructure module and the sensormodule operable to supply power from the electricity generated by theheterostructure module back to the heterostructure module to causeemission of the output light and to receive the electrical sensor signalfrom the sensor module and the heterostructure module is structured toproduce that output light that is modulated to carry the electricalsensor signal to wirelessly and optically transmit the electrical sensorsignal out of the device.

In yet another aspect, for example, the disclosed technology can beimplemented to provide a device with opto-electronic circuitry thatincludes a substrate, a photovoltaic module engaged to the substrate andstructured to convert light into electricity, a sensor module engaged tothe substrate and coupled to receive power from the electricitygenerated by the photovoltaic module, the sensor module structured toinclude a sensing element that is responsive to a target substance toproduce a response, wherein the sensor module is further configured togenerate, based on the response from the sensing element, an electricalsensor signal indicative of a property of the target substance, and alight-emitting module photolithographically formed to the substrate tohave a dimension less than 40 microns and coupled to receive power fromthe electricity generated by the photovoltaic module and to receive theelectrical sensor signal from the sensor module, the light-emittingmodule structured to produce output light that is modulated to carry theelectrical sensor signal to wirelessly and optically transmit theelectrical sensor signal out of the device.

In yet another aspect, the disclosed technology can be implemented toprovide an optical wireless sensor device that includes a photovoltaicmodule structured to convert electromagnetic radiation into electricity,a sensor module coupled to the photovoltaic to receive the electricitygenerated by the photovoltaic module and structured to include a sensingelement and a communication element, the sensing element beingresponsive to a target substance to produce a response, thecommunication element being configured to generate, based on theresponse from the sensing element, an electrical sensor signalindicative of a property of the target substance, and a light-emittingmodule coupled to the photovoltaic module to receive the electricity andcoupled to the sensor module to receive the electrical sensor signal andconvert the electrical sensor signal to output electromagnetic radiationindicative of the property of the target substance.

In yet another aspect, the disclosed technology can be implemented toprovide a device with opto-electronic circuitry, comprising: asubstrate; a photovoltaic module engaged to the substrate and structuredto convert light into electricity; an identification module engaged tothe substrate and coupled to receive power from the electricitygenerated by the photovoltaic module, the identification moduleconfigured to generate an electrical identification signal indicative ofan identity of the device; and a light-emitting module engaged to thesubstrate and coupled to receive power from the electricity generated bythe photovoltaic module and to receive the electrical identificationsignal from the identification module, the light-emitting modulestructured to produce output light that is modulated to carry theelectrical identification signal to wirelessly and optically transmitthe electrical identification signal out of the device.

Yet another aspect, the disclosed technology can be implemented toprovide a device with opto-electronic circuitry, comprising: asubstrate; a photo-electronic module engaged to the substrate andstructured to convert light into electricity; and an identificationmodule engaged to the substrate and coupled to receive power from theelectricity generated by the photo-electronic module, the identificationmodule configured to generate an electrical identification signalindicative of an identity of the device, wherein the photo-electronicmodule is configured to receive the electrical identification signalfrom the identification module and produce output light that ismodulated to carry the electrical identification signal to wirelesslyand optically transmit the electrical identification signal out of thedevice.

Yet another aspect, the disclosed technology can be implemented toprovide a device with opto-electronic circuitry, comprising: asubstrate; a photovoltaic module engaged to the substrate and structuredto convert input light into electricity, the photovoltaic modulestructured to include a sensing element that is responsive to a targetsubstance to produce a response, wherein the photovoltaic module isfurther configured to generate, based on the response from the sensingelement, an electrical sensor signal indicative of a property of thetarget substance; and a light-emitting module engaged to the substrateand coupled to receive power from the electricity generated by thephotovoltaic module and to receive the electrical sensor signal from thephotovoltaic module, the light-emitting module structured to produceoutput light that is modulated to carry the electrical sensor signal towirelessly and optically transmit the electrical sensor signal out ofthe device.

Yet another aspect, the disclosed technology can be implemented toprovide a device with opto-electronic circuitry, comprising: asubstrate; a photovoltaic module engaged to the substrate and structuredto convert input light into electricity; and a light-electrical signalconversion module engaged to the substrate and structured to receivepower from the electricity generated by the photovoltaic module, thelight-electrical signal conversion module being responsive to a targetsubstance to produce an electrical sensor signal indicative of aproperty of the target substance, the light-electrical signal conversionmodule being structured to produce output light that is modulated tocarry the electrical sensor signal to wirelessly and optically transmitthe electrical sensor signal out of the device.

The above and other aspects and implementations of the disclosedtechnology are described in more detail in the drawings, the descriptionand the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1E show a method of polymer-assisted transfer of AlGaAs systemheterostructures to other substrates.

FIGS. 2A-2B show examples of AlGaAs heterostructure light-emitting diodeused for transfer.

FIG. 3 illustrates an example planar alignment method ofpolymer-assisted transfer of AlGaAs system heterostructures to othersubstrates.

FIG. 4 shows an example of AlGaAs light-emitting diodes transferred tosilicon substrate and adhered to the surface using a thin, conformaloxide.

FIGS. 5A-5F show an example lithographic integration of silicon CMOScircuitry and AlGaAs heterostructure for optically-powered andoptically-readout neuron sensors.

FIG. 6 shows substrate and example fabrication enabling integration ofreleasable silicon and AlGaAs heterostructures.

FIGS. 7A-7D shows optical images and performance of micron-scale exampleconfigurations including silicon MOSFETs, silicon photovoltaics, andAlGaAs LEDs fabricated on the same substrate.

FIG. 8 shows example substrate and fabrication method schematics.

FIGS. 9A-9D show example substrate and fabrication method schematicsillustrating a perspective view for releasable, sub-mm³ devices.

FIGS. 10A-10D show examples of large-scale integration of micron-scalesilicon and III-V electronics and optoelectronics for releasabledevices.

FIGS. 11A-11F show an example integrated circuit of GaAs LED and siliconMOSFET.

FIGS. 12A-12F show examples of optically powered voltage sensorfabrication on a release-compatible substrate.

FIGS. 13A-13E show example wireless, optically powered, cell-scalesensor systems and applications.

FIG. 14 shows an example alternative release method for integrated CMOSand AlGaAs heterostructure cell-scale sensors.

FIGS. 15A-15D illustrate examples of sensors made by using large-scaleintegration of micron-scale silicon and III-V electronic andoptoelectronics for releasable devices.

FIGS. 16A-16G show examples of wireless, optically poweredoptoelectronic cell-scale sensors.

FIGS. 17A-17B show a block diagram of the system and a schematic of theamplifier that boosts the differential signal between the two sensingelectrodes that are spaced ˜150 μm apart to sample the electric fieldsgenerated by nearby neurons.

FIGS. 18A-18D show that the amplifier drives the pulse-position encoder,while a 10 KHz relaxation oscillator generates a periodic pulse, whichcharges capacitor C1 to VDD.

FIGS. 19A-19B show example measurement of optical output pulse (FIG.19A), and associated reconstructed 1 KHz waveform (FIG. 19B). FIGS.19C-19D show signal gain as a function of frequency (FIG. 19C) andamplitude (FIG. 19D).

FIGS. 20A-20B show start-up, showing onset of optical pulses (FIG. 20A)and decoded signal (FIG. 20B). FIGS. 20C-20S show neural recording on anearthworm ventral nerve upon mechanical stimulation measured in parallelthrough a commercial amplifier to provide baseline (FIG. 20C) and usingthe presented system, powered and communicating optically (FIG. 20D).

FIG. 21 shows a breakdown of the design by power consumption and by Siarea.

FIG. 22 shows an example of the optical wireless integrated circuitsensor implemented based on some embodiments of the disclosedtechnology.

FIG. 23 shows an example of the optical wireless sensor deviceimplemented based on some embodiments of the disclosed technology.

FIG. 24 shows an example of the optical wireless sensor deviceimplemented based on some embodiments of the disclosed technology.

FIG. 25 shows an example of the optical wireless identification deviceimplemented based on some embodiments of the disclosed technology.

FIG. 26 shows an example of pulsed-position modulation (PPM) encoding

FIG. 27 shows an example method for sensing a target subject.

FIG. 28 shows an example layout and implementation of a wireless opticalidentification device based on the disclosed technology.

DETAILED DESCRIPTION

Wireless devices for sensing, actuation, and identification areincreasingly desired for smart packaging, medical sensors, and tracking.Some existing implementations of wireless systems are primarily poweredby and communicate with RF coils or ultrasound. Size-scale requirementsfor such power sources fundamentally limit the size at which they can beproduced. Furthermore, in some implementations, the techniques toconstruct such wireless sensors typically involve using dicing saws todice materials, manually or serially stacking the material systems,and/or establishing electrical interconnects with wire-bonding orflip-chip bonding or using solder microbumps. These techniques can limitthe size-scales and parallel production of devices and it is difficultto use such techniques to produce compact devices, such as thosesignificantly smaller than 1 mm³.

The disclosed technology in this patent document can be used toconstruct wireless sensors or/and wireless devices with opto-electroniccircuitry that converts light into electricity for powering the devicesand also generates output light that is modulated to carry informationfrom the sensor operation so that such a sensor device is not linked toany physical connection outside the sensor device (e.g., a wire orcable) for versatile sensing and identification applications usingwire-free devices. For example, in some embodiments of the disclosedtechnology, a wireless method for monitoring electrical and chemicalsignals at the individual cell level would allow for uses of wire-freedevices with opto-electronic circuitry to provide wireless opticaloutput of various sensor measurements ranging from mapping neuralactivity in the brain to detecting the release of neurotransmitters.Examples are disclosed for a transfer method, substrate, and devicesenabling wireless, inorganic cell-scaled sensor systems that areoptically powered, optically readout, and capable of monitoringelectrical and chemical signals.

Recording neural activity in live animals in vivo poses severalchallenges. Electrical techniques typically require electrodes to betethered to the outside world directly via a wire, or indirectly via anRF Coil, which is much larger than the electrodes themselves. Tetheredimplants result in residual motion between neurons and electrodes as thebrain moves and limit our ability to measure from peripheral nerves inmoving animals, especially in smaller organisms such as zebra fish orfruit flies. On the other hand, various implementations of opticaltechniques, which are becoming increasingly powerful, are nonethelessoften limited to subsets of neurons in any given organism, impeded byscattering of the excitation light and emitted fluorescence, and limitedto low temporal resolution. This patent document discloses examples ofdesigns of the electronics for an untethered electrode unit, powered by,and communicating through a microscale optical interface, combining manybenefits of optical techniques with high temporal-resolution recordingof electrical signals.

Some embodiments of the disclosed technology can be used to transfer andadhere AlGaAs system heterostructures to other substrates with one ormore of the following unique features. Firstly, the disclosed technologycan be used for transferring AlGaAs material system heterostructures toa wider variety of substrates. In addition to substrates such assilicon, glass, III-Vs, metals, flexible materials (PET, PDMS), etc.,the disclosed technology can be used to transfer high-curvatureobjections like micron-scale needles, optical-fibers, microlens, etc. todesired final substrates. Secondly, unlike various other transfermethods that require that mesa structures be of the same or similarshape and size for each transfer, the disclosed method ofpolymer-assisted transfer of AlGaAs system heterostructures to othersubstrates may transfer a plurality of heterostructures of arbitraryshapes in varying sizes (e.g., from nanometers to 1 millimeter) in thesame transfer process. Thirdly, unlike some implementations of transferprinting, which is a widely-used method for the transfer of micro-LEDsand other optical heterostructures, there is no need to tune the speedof delamination of a transfer stamp for pick-up and transfer inimplementing the transfer under the disclosed technology in this patentdocument. The tuning of these parameters for consistent results andhigh-yield can be difficult. In addition, it can also be very difficultto transfer optical heterostructures of thickness less than 1 micron orthose of non-rectangular shapes, such as parabolically shaped microLEDs. The disclosed example for the polymer-assisted transfer method ofAlGaAs system heterostructures may enable the transfer of such opticalheterostructures in thin structures, including structures as thin as 900nm, for example. Furthermore, optical heterostructures are adhered tosilicon and other substrates using conformal dielectrics. Thesedielectrics can be thinner than many adhesive materials, and silicondioxide, silicon nitride, and other dielectrics can be deposited at ananometer scale and precision using atomic layer deposition, forexample. These dielectrics also are stable at high temperatures (e.g.,hundreds of degrees Celsius). These unique features contrast those ofthick epoxies which are not compatible with high temperature processingstandard to many semiconductor processes.

Some embodiments of the disclosed technology can be implemented toprovide a substrate and fabrication method that enable the integrationof silicon electronics (MOSFETs, photovoltaics, resistors, capacitors,JFETs, BJTs, etc.) and aforementioned transferred AlGaAsheterostructures at the micron-scale for releasable, wirelesscell-scaled devices. The substrate and fabrication method can beimplemented with one or more of the following unique features. Firstly,a PN-junction or PNP-junction is made and activated in the device layerof a silicon on insulator substrate prior to transfer of opticalheterostructures. This avoids incompatibilities in thermal budgets thattypically make standard silicon electronic fabrication methodsincompatible with the AlGaAs system. This also enables high-performance,nanometer- or micron-scaled silicon electronics to be patterned inalignment to AlGaAs heterostructures in the same fabrication process.Secondly, the substrate and fabrication method disclosed in this patentdocument allows for the AlGaAs heterostructures to be separatelyoptimized from the silicon fabrication process. An integration processof devices using gallium-arsenide grown on silicon are not as efficientas AlGaAs systems separately optimized and grown, and the performance ofthe two components typically suffers. Moreover, the methods based on thedisclosed technology can provide technical solutions to fabricationissues that are difficult to solve by using various known fabricationtechniques or processes such as those for releasing fabricatedstructures or devices. Thirdly, it is possible to transfer III-Vheterostructures onto silicon CMOS devices to make integrated deviceswith better performance, but the method of polymer-assisted transfer ofAlGaAs system heterostructures is superior to existing methods becausethe polymer-assisted transfer of AlGaAs system heterostructures can bemade in a manner that enables a releasable device at cell-scale.Moreover, the designs for various sensor and/or identification devicesdisclosed in this patent document may be formed using many differentdesigns integrating silicon and AlGaAs systems with tens of thousands ofintegrated circuits (ICs) on every chip.

Some embodiments of the disclosed technology can be implemented toprovide wireless, optically powered inorganic optoelectronics forcell-scaled devices that can receive information optically and opticallycommunicate information out. The optically powered devices implementedbased on some embodiments of the disclosed technology may be enabled bythe aforementioned methods and substrates. The optically powered devicesmay be structured to include one or more unique features including thefollowings. For example, the optically powered devices implemented basedon some embodiments of the disclosed technology can be wireless,inorganic cell-scaled devices with optical-power using micron-scalephotovoltaics. These devices can also be structures to convertelectrical signals into an optically readout signals using micro-LEDs(or other optical heterostructures). Furthermore, the optically powered,wireless, inorganic cell-scaled devices can be configured to allowuntethered, wireless optical-communications using encoded light read andusing micron-scale photovoltaics. In some implementations, the opticallypowered, wireless, inorganic systems based on the disclosed technologycan be made at the cell-scale or other desirable scales suitable forspecific applications. The cell-scale or miniaturized scales can be usedto enable injection of the device while causing little to no tissuedamage if intended for biological systems. The optically powered devicesalso allow for high-speed (greater than kHz) detection of signalsoptically using a wireless system that can be made at the cell-scale.This feature is in contrast to other imaging techniques, for example,calcium imaging of cells. By using the fabrication methods disclosed inthis patent document, thousands to millions of devices can be implantedat arbitrary locations without fixed relative distances to one another.In addition, signal multiplexing in time of the communication out andoptical carrier wavelength of the output signal allows for monitoring ofpotentially a large number of sensor and/or identification devices(e.g., more than a thousand of sensor devices) simultaneously, thusachieving parallel sensor measurements and processing.

Some methods based on the disclosed technology for millimeter-scaled,untethered sensors and identifications may implement a suitable powertechnology, including, for example, the RF-coil power, on-boardbatteries, or ultrasonic-powering using piezo-electronics. The disclosedtechnology can be used to integrate micron-scale photovoltaics with LEDsas a method of enabling an optically powered, optically readout sensormade at the cell-scale. This aspect of the disclosed technology enablesseveral features such as: power to be supplied externally using light;information to be supplied to the sensor using light; and for the deviceto communicate out information via light. By using electromagneticradiation, an immense amount of power can be concentrated into anextremely small, down to the nanoscale, volume, and communication can beachieved at the fastest speeds possible. In addition, the devices, theircommunication, and their powering can be electrically decoupled from thesystem if desirable.

Sensor and/or identification devices based on the disclosed technologycan be used to enable optically powered, optically controlled, opticallyreadout current sources, voltages source, voltage sensors, and currentsensors to be integrated into the same releasable system. The disclosedtechnology enables cyclic-voltammetry (fast-scan cyclic voltammetry,ultramicroelectrode voltammetry, etc.) that can be performed in acell-sized volume of fluid with the sensor system within the fluid. Thisenables uses such as neurotransmitter detection at the individualcell-scale. Additionally, by detecting chemical species in smallvolumes, a small-sample can provide enough material for a largermultitude of tests in cases. This may be of great use in cases wheresample volume is limited. The disclosed technology also providescell-scale voltage sensors that can be made to detect electrical signalsfrom individual neurons, cardiac cells, etc. The disclosed technologycan be further implemented to detect cell-scale ionic currents throughcell-membranes, nano-constrictions, or microfluidic channels. Thedisclosed technology may also enable voltages and currents to be appliedto solutions to stimulate cells or neurons using cell-scaled systems.

Examples of the Transfer Method in Fabrication

Materials used for efficient light-emitting structures are often not thesame as those materials used for high-performance electronic devices. Inan embodiment of the disclosed technology, silicon may be used toconstruct high-performance transistors (e.g., MOSFETs, BJTs, JFETs,etc.) that form the structures implemented based on some embodiments ofthe disclosed technology. The indirect band gap of silicon, however, maymake it inefficient as a material for emitting light. In anotherembodiment of the disclosed technology, AlGaAs light-emitting diodeheterostructure can be used for transfer. Although the AlGaAs system isnot typically used to produce transistors in modern electronics, theymay be used to produce high-efficiency light-emitting diodes (LEDs) andlasers. Embodiments could also include, more specifically, resonantcavity LEDs (RCLEDs) and vertical-cavity surface-emitting laser(VCSELs).

The disclosed heterostructures may be implemented by combining twomaterial systems such as silicon and AlGaAs at the micron-scale toenable hybrid optoelectronics utilizing high-performance electronics andefficient light-emitting components. Many methods including transferprinting, wafer bonding, ball-bonding, and epitaxial liftoff exist toattempt to address this desired goal. Each method for transfer comeswith its own advantages and disadvantages over the alternatives. Variousimplementations of these existing techniques have not been able toconstruct wireless sensors at the cellular-scale.

Various embodiments of the disclosed technology provide a novel methodof transferring AlGaAs system heterostructures to other substrates asshown schematically in FIGS. 1A-1E. FIGS. 1A-1E show an example methodof polymer-assisted transfer of AlGaAs system heterostructures to othersubstrates. In an implementation of the disclosed technology, a methodof transferring AlGaAs systems (or any other sufficiently GaAslattice-matched systems, such as AlGaAs, AlGaInP, GaP, and GaAsP) tovarious substrates starts with patterned or un-patternedheterostructures composed of various AlGaAs layers on a release layer ofAl_(y)Ga_(1-y)As, where y is between 0 and 1 and such that the releaselayer can be etch with sufficient selectivity against etching of thedevices to be transferred and is sufficiently selective against theetching of the substrate. FIG. 1A illustrates a film of polymer (e.g.,polymethyl methacrylate: PMMA) is spun and cured, covering the devicesto be transferred. FIG. 1B illustrates the GaAs substrate is etched in amixture of citric acid and hydrogen peroxide at a ratio that selectivelyetches the GaAs substrate more rapidly than the Al_(y)Ga_(1-y)As releaselayer. The release layer and polymer protect the devices to betransferred from being etched. FIG. 1C shows the release layer is thenetched in a dilute mixture of hydrofluoric acid (HF) which is selectiveagainst etching the AlGaAs heterostructures. FIG. 1D illustrates, aftertransferring the polymer-encased devices through a DI bath to remove anycontaminants, the polymer film can be transferred to a new substrate. Ifneeded, as shown in FIG. 1E, the polymer can then be removed with a dryetch such as reactive ion etching using oxygen plasma. For adhesion tothe substrate, conformal dielectrics such as SiO2 can be deposited. Inanother embodiment, the Al_(y)Ga_(1-y)As release layer can beselectivity etched (with, e.g., HF) without need to etch the GaAssubstrate. This may have benefits for particular applications with theGaAs substrate is desired for reuse.

FIGS. 2A-2B show examples of AlGaAs heterostructure light-emitting diodeused for transfer. Specifically, FIG. 2A shows a table detailingmaterial, thickness, dopant, and concentration of AlGaAs system layersused to produce light-emitting diodes. Some embodiments of the disclosedtechnology can be used to transfer AlGaAs system heterostructures(light-emitting diodes, lasers, transistors, etc.) to arbitrarysubstrates (silicon, glass, PET, optical fibers, etc.). By way ofexample and not by limitation, the disclosed technology can be used totransfer AlGaAs micro-LEDs to a silicon substrate.

FIG. 2B shows cross-section of the layers of the AlGaAs light-emittingdiode on the intermediate release layer and GaAs substrate implementedbased on some embodiments of the disclosed technology. To begin, anAlGaAs heterostructure is grown by a metalorganic chemical vapordeposition (MOCVD). The series of layers can be broken into threefundamental portions, including substrate, release layer, andheterostructure. In an implementation, the substrate is a thick,few-hundred-micron, wafer of intrinsic GaAs, and the release layer is athin, few-hundred nanometer, layer of Al_(0.9)Ga_(0.1)As. In animplementation, the heterostructure is a series of layers grown on topof the release layer composed of contact layers, cladding layers, and anemission region where electron-hole pairs combine to emit light. In thiscase, the optical heterostructure is an LED with multiple quantum wellsfor increased efficiency of electron-hole recombination.

After growth of the optical heterostructure on the release layer, theAlGaAs heterostructures are then pattern into micron-scaled LEDs(micro-LEDs) of various sizes and shapes with metal contacts forelectrical interconnects to the anode and cathode. A thin layer ofpolymer is spun onto the micro-LEDs and cured using standardphotolithography techniques. In an embodiment of the disclosedtechnology, a 1.5 micron thick layer of poly (methyl methacrylate)(PMMA) is spun onto the topside of the substrate, covering themicro-LEDs. At this stage of the fabrication, there is an array ofmicro-LEDs patterned on top of the Al_(0.9)Ga_(0.1)As release layer,coated with a thin layer of polymer as shown in FIG. 1A. The thinpolymer layer serves to protect the micro-LEDs during the etch steps tofollow and provide a frame fixing the relative location of themicro-LEDs.

In some embodiments of the disclosed technology, the next step utilizesthe varying etch rates of different compositions of Al_(x)Ga_(1-x)Aswith x between 0 and 1. Depending on the composition of theAl_(x)Ga_(1-x)As, the etch rate in different chemical solutions can varyby orders of magnitude. For example, Al_(0.9)Ga_(0.1)As etches muchslower in 4:1 citric acid:hydrogen peroxide than GaAs, whereas inhydrofluoric acid Al_(0.9)Ga_(0.1)As etches much more rapidly than GaAs.A PMMA covered substrate is placed in a mixture of 4:1 citricacid:hydrogen peroxide for an extended period (e.g., about 20 hours for500 micron thick substrates). The etch is so selective for GaAs andagainst Al_(0.9)Ga_(0.1)As that in the time needed to etch the entiresubstrate, most of the Al_(0.9)Ga_(0.1)As layer remains. This step isshown schematically in FIG. 1B. Both the Al_(0.9)Ga_(0.1)As releaselayer and the PMMA serve to protect the AlGaAs optical heterostructureduring this etch.

As shown in FIG. 1C, following the etch of the GaAs substrate, theremaining PMMA/heterostructure/release layer system is transferred to adilute hydrofluoric acid (HF):deionized water (DI) mixture (50:1 HF:DI).This selectively etches the Al0.9Ga0.1As release layer at a much higherrate than the micro-LEDs allowing for the release layer to be removedcompletely before the micro-LEDs have been etch any appreciable amount.

The remaining PMMA film containing the micro-LEDs is then passed througha cleaning process using, e.g., deionized (DI) water to removecontaminants before being transferred to a silicon substrate as shown inFIG. 1D. In this case, the transfer substrate is thePN-junction-containing silicon on insulator substrate described in theproceeding text. The sample is then dried in air on at a slightlyelevated temperature on a hotplate.

FIG. 3 illustrates an example alignment method of polymer-assistedtransfer of AlGaAs system heterostructures to other substrates. Ifalignment of the AlGaAs heterostructures to the transfer substrate isneeded, the transfer method can be adapted to aligned transfer. In oneembodiment, a polymer, e.g. PMMA, is spun onto the AlGaAs opticalheterostructures and cured (310). The AlGaAs optical heterostructuresare on an AlGaAs release layer grown on a GaAs substrate as discussedabove. A thermal release layer is spun onto the PMMA and used to bondthe GaAs substrate to a carrier substrate (320). The carrier substratecan be any rigid structure partially transparent to visible or IR light.The thermal release layer is chosen such that the material can beremoved at temperatures that do not remove or melt the PMMA. Examples ofsuch materials include polypropylene carbonate (PPC) which can beremoved at temperatures well below PMMA's melting point of 160 degreesCelsius. In another embodiment, this thermal releaser layer can bemodified to be replaced by a thermal or ultra-violet (UV) release tapeoften using for semiconductor wafer dicing processes. Such tapes alsoreduce their adhesion force after being exposed to heat or UV light. Thebonded substrates are placed in the wet etches described above to removethe GaAs substrate and AlGaAs release layer (330). Using the rigidcarrier substrate, the AlGaAs optical heterostructures in PMMA can bealigned and bonded to the desired transfer substrate (340). By heatingthe system to a high enough temperature following alignment, the thermalrelease layer is removed allowing for the removal of the carriersubstrate without removing the PMMA or AlGaAs optical heterostructures(350).

At this point in the process, the polymer can be removed completely orpatterned by standard dry or wet etching techniques (360). For example,reactive-ion etching using an oxygen plasma can serve to remove PMMAwithout damaging the micro-LEDs. Using a dry etch technique allows forthe micro-LEDs to remain with their relative locations, adhered to thesubstrate by van der Waals interactions.

If further adhesion is needed, a conformal layer of insulation materialcan be deposited adhering the micro-LEDs to the substrate (360), as alsoshown schematically in FIG. 1E. In one embodiment, atomic-layerdeposition (ALD) can be performed using dielectrics such as silicondioxide to adhere the micro-LEDs to the substrate. In anotherembodiment, plasma enhanced chemical vapor deposition (PECVD) can beperformed to produce dielectrics such as silicon dioxide and siliconnitride.

If even further adhesion is desired, a thin layer of SU8 (can bedeposited below 10 micron thickness), can be deposited and patternedprior to transfer. Either as deposited or under small amounts of heat,the SU8 layer can serve as a bonding layer between the light-emittingelement and the substrate.

In another embodiment, if further adhesion is desired, lowmelting-temperature metals such as Rose's metal, or metals with strongbonding properties to AlGaAs such as palladium can be used to promoteadhesion.

FIG. 4 shows an example of AlGaAs light-emitting diodes transferred tosilicon substrate and adhered to the surface using a thin, conformaloxide. LEDs of various sizes and shapes were transferred during the sametransfer. Scale-bar, shown bottom-left, is 200 microns. Micro-LEDs shownare 900 nm in thickness and a variety of shapes and sizes. The methoddescribed above can be used to transfer micro-LEDs to various substratesincluding silicon, glass, metal, plastics, polymers, and micron-scaleneedles. Micro-LEDs of various sizes can be transferred to a siliconsubstrate and adhered using ALD silicon dioxide.

FIGS. 5A-5F show an example integration of silicon CMOS circuitry andAlGaAs heterostructure for optically-powered and optically-readoutneuron sensors. Specifically, FIG. 5A illustrates schematic of apossible application enabled by the methods discussed above. The sensordevice in FIG. 5A is shown as being embedded in an organ or tissuewithout wire attached and, as illustrated in the enlarged view, includesa photovoltaic module for receiving illumination light for convertingthe received illumination light into electricity to power the CMOS senorcircuitry with one or more amplifiers and a signal encoder, and anoptical transmitter for generating the optical output that is modulatedto carry sensor data. An optical illumination light source is placedoutside the tissue to illuminate the area of the tissue where the sensordevice is located. In this specific example, an optical beam splitter isprovided in the optical path between the tissue and the illuminationlight source to split the illumination light into a monitor beam to anoptical monitor such as a photodiode (PD) and an illumination beam tothe tissue. The optical monitor is used to adjust the intensity of theillumination light based on the monitor beam, thereby adjusting theintensity of the light illuminated on the photovoltaic module in thesensor device. The illumination beam output from the optical beamsplitter is directed to the tissue using an optical projection modulelocated between the optical beam splitter and the tissue. Thephotovoltaic module in the sensor device converts received illuminationlight into electricity that is used to energize various components inthe sensor device, including, for example, a sensor that interacts withthe tissue to obtain desired measurements in form of a sensor signal, asignal encoder that is used in encoding the sensor signal into a properform for being modulated onto the output light generated by the opticaltransmitter. The sensor can optically send out the output light, whichis modulated to carry the sensor signal, from the tissue so that anoptical detection module outside the tissue can detect the sensorsignal. In an implementation, the illumination light may include acontinuous wave with a wavelength that is shorter than that of theoutput light. Some embodiments of the disclosed technology can beimplemented to provide a cell-scale sensor that is capable of monitoringelectrical signals from neurons by being injected into the tissue of thebrain, optically powered via one wavelength and optically-readout usinganother wavelength. The particular GaAs heterostructure implementedbased on some embodiments of the disclosed technology is capable ofbeing a dual-purpose photovoltaic and LED (PVLED). Hence, onceintegrated, the photovoltaic provides power, the silicon circuitrymeasures, amplifies, and encodes the signal, and finally, the signal isoptically communicated out using the LED functionality of the PVLED.

FIG. 5B shows performance of the dual-purpose PVLED, with I-V curves ofa custom, dual-functioning AlGaAs photovoltaic/light emitting diode(PVLED) unit in its PV and LED modes. When mounted on top of a CMOS die,about 98% of the time, the PVLED acts as a power source, transducingincoming light into electrical power, providing at least 1 μA at ˜0.9V.During the remaining 2% of the time, the PVLED acts as an opticaltransmitter, emitting optical pulses to transmit the measured data to anexternal receiver at a longer wavelength. This allows the system to bemore compact than the previously reported RF and ultrasonic approaches.

FIG. 5C shows an optical image of an integrated device with the AlGaAsPVLED transferred on top of electrical interconnects of a silicon CMOScircuit, depicting the integration of the PVLED on 180 nm CMOS where theunderlying CMOS circuitry incorporates recording electrodes,amplification, pulse-position encoding, and a PVLED interface toarbitrate power and communications. The dual-purpose PVLED implementedbased on some embodiments of the disclosed technology includes an AlGaAsphotovoltaic/light emitting diode, an anode and a cathode of the AlGaAsphotovoltaic/light emitting diode, and plus and minus inputs of CMOScircuitry formed on the CMOS die. In some embodiments of the disclosedtechnology, metal interconnects are patterned to electrically connectthe anode and cathode of the AlGaAs photovoltaic/light emitting diode tothe corresponding connections of the CMOS circuitry. Notably, the metalinterconnects can be photolithographically formed such that the metalinterconnects can have a smallest dimension under 10 microns anddistances between electrodes are less than 40 microns. The dual-purposePVLED implemented based on some embodiments of the disclosed technologycan be formed by transferring AlGaAs optical heterostructure to CMOScircuitry using the disclosed methods. Since neural tissue is primarilyscattering (as opposed to absorbing), such a system can, in principal,function at depths greatly exceeding that of imaging, but without thetethers required by most electrodes. The device is then connectedelectrically using standard photolithography. FIG. 5D shows layout ofthe CMOS circuitry underneath the top metal contacts includingcomponents such as inputs VIN− and VIN+, an amplifier, circuitrygenerating a proportional to absolute temperature current PTAT,circuitry for start-up STARTUP, a pulse generator PULSE GEN, MOScapacitors MOS CAP, an LED driver LED DRIVER, and encoding circuitryENCODER. FIGS. 5E and 5F show comparison performance of a commercialamplifier to the silicon-PVLED system wired together.

As another illustration of the scope of use for this transfer method,this patent document provides an example where a dual-purposephotovoltaic/light-emitting diode (PVLED) is aligned, transferred, andintegrated into a complex silicon complementarymetal-oxide-semiconductor (CMOS) circuit shown in FIGS. 5C and 5D. Theintegrated device, enabled by this transfer method, is the first exampleof a wireless, optically powered and optically-readout inorganiccell-scaled sensor capable of monitoring neural activities.

The transfer of AlGaAs heterostructures transferred to both unpatternsilicon and full CMOS silicon substrates is discussed in this patentdocument by way of example and not by limitation, and thus the method oftransfer allows for many different embodiments. Using the same transfermethod, both the type of heterostructure and the substrate can bevaried. The possibilities for heterostructures that are capable oftransferring using this method include, but are not limited to,light-emitting diodes, lasers, photovoltaics, and transistors. Someexamples of transferable heterostructures include: near-infrared GaAslasers; red AlInP light-emitting diodes; AlGaAs photovoltaics; infraredInP lasers; and AlGaAs/GaAs high-electron-mobility transistors (HEMTs).

The substrate to which AlGaAs heterostructures can be transferred canalso be varied. The possibilities for substrates to which the AlGaAsheterostructures can be transferred to using this method include, butare not limited to: semiconductors (silicon, AlGaAs, silicon carbide,sapphire, etc.); metals (gold, platinum, aluminum, etc.); dielectrics(silicon dioxide, aluminum oxide, silicon nitride, etc.); flexiblesubstrates (PMMA, Polydimethylsiloxane, Polyethylene terephthalate,etc.); and high-curvature objects (microneedles, optical fibers,microlens, etc.)

Although the above disclosed examples of fabrication methods are for theAlGaAs material system, the methods disclosed can be adapted to devicefabrication with other III-V semiconductor material systems such as GaNand InGaN. The above methods are implemented by using a material thatcan be used as the release layer which (1) is sufficiently latticematched to the material system to be grown on it and (2) is selectivelyetchable with respect to the optical heterostructures layer in contactwith it. In the example disclosed above, the Al_(0.9)Ga_(0.1)As servedas the latticed matched release layer and was etched selectively withhydrofluoric acid with respect to the n-type GaAs in contact with theAl_(0.9)Ga_(0.1)As. In another embodiment, GaN or InGaN opticalheterostructures could be grown on (111) silicon release layer which canbe selectively etched using potassium hydroxide. In another embodiment,GaN or InGaN optical heterostructures could be grown on heavily dopedGaN layer with an electric bias applied to it allowing for selectiveetching in oxalic acid or other electrolyte solutions such as potassiumhydroxide or hydrochloric acid. The disclosed methods hence enablefabrication of optoelectronic circuitry to include light emittingmodules using III-V material systems including, e.g., GaAs, AlGaAs, GaP,InGaP, InGaAsP, GaN, AlGaN, or InGaN.

Examples of Substrates Used in Fabrication

Examples of a substrate and fabrication method integrating AlGaAsoptical heterostructures and silicon electronics, enabling wireless,optically powered inorganic optoelectronics for cell-scaled sensors willbe discussed below. The optical images and data from example sensorsfabricated using some embodiments of the disclosed technology will alsobe discussed below.

There are three primary challenges to integrating AlGaAs opticalheterostructures and silicon electronics at the micron-scale forwireless, optically powered inorganic optoelectronics for cell-scaledsensors. First, the two materials systems, silicon and AlGaAs, are notlattice-matched and hence high-efficiency optical heterostructures andhigh-performance silicon electronics cannot be readily grown on the samesubstrate. Secondly, the elevated temperature typically required forsilicon electronics would damage most AlGaAs optical heterostructures.The second challenge is most notable when considering dopant activationfor dopants in silicon. In modern silicon electronics, both n-type andp-type dopants are implanted into a silicon substrate using varioustechniques including ion-implantation and diffusion. Following theimplantation of these dopants, the dopants typically must be activatedat temperatures above 1000 degrees Celsius. Although materials like thesilicon dioxide and silicon can withstand these elevated temperatureswithout damage, AlGaAs optical heterostructures often degrade at suchtemperatures. For example, at temperatures above 600 C, diffusion canoccur in our AlGaAs micro-LEDs that damages the quantum wells in theemission region, reducing efficiency. There is no established method bywhich one could make wireless, cell-scale, integrated optoelectroniccircuits on a typical silicon and AlGaAs substrate that can be releasedfrom the substrate.

A solution to the first challenge has been addressed in this patentdocument, including the transfer method that allows for the growth ofthe AlGaAs optical hetero structure on a separate GaAs (or similarlylattice-matched) substrate before transfer to another substrate. Thesecond and third challenges can also be overcome by using a substratethat allows for high-performance silicon electronics but requires noadditional anneals at temperatures above 600 degrees Celsius after thetransfer of AlGaAs optical heterostructures. Furthermore, the substrateand fabrication method can enable the final integrated, cell-scaledevices to be released from the handle substrate.

In one embodiment of the substrate, we begin with a silicon on insulator(SOI) substrate consisting of a thick 500 micron silicon handle, a thin500 nanometer buried oxide (BOX), and a 2 micron-thin p-type silicondevice layer. A thin, 500 nanometer, layer of phosphosilicate glass(PSG) is deposited on the silicon device layer and then the substrate isannealed at 1050 degrees Celsius for approximately 5 minutes. Thisanneal both drives in the phosphorus dopants partially through thesilicon device layer and activates them. The remaining PSG glass is thenremoved in a buffered oxide etch (BOE). At the point the substrateconsists of a SOI wafer with a PN-junction formed in the silicon devicelayer.

Using the transfer method disclosed above, AlGaAs heterostructures canbe transferred and adhered to the PN-junction-containing SOI wafer.Because the PN-junction has been formed everywhere on the surface of thesubstrate, the surface of the substrate is horizontally symmetric andhence no aligned transfer is needed to the substrate.

FIG. 6 shows substrate and example fabrication enabling integration ofreleasable silicon and AlGaAs heterostructures, including: PN-junctionSOI wafer with AlGaAs heterostructure before etching and metal contacts(610); PN-junction SOI wafer with AlGaAs heterostructures and siliconelectronics after etching and metal contacts (620) (example siliconelectronics possible shown include photovoltaics (PVs), nMOS MOSFETs,NPN BJTs, n-channel JFETs, MOS capacitors, and silicon resistors;NPN-junction SOI wafer with AlGaAs heterostructure before etching andmetal contacts (630); and NPN-junction SOI wafer with AlGaAsheterostructures and silicon electronics after etching and metalcontacts (640) (example silicon electronics possible shown includephotovoltaics (PVs), nMOS MOSFETs, pMOS MOSFETs, NPN BJTs, PNP BJTs,n-channel JFETs, p-channel JFETs, MOS capacitors, and siliconresistors).

Following the transfer and adhering of the AlGaAs heterostructures tothe PN-junction containing SOI wafer, various silicon electronics can befabricated aligned to the AlGaAs heterostructures down to the nanoscaleby etching the silicon device layer to the desired depth and makingelectrical contact to the n-type and/or p-type silicon within the devicelayer. As shown in FIG. 6, the silicon devices that can be integratedwith AlGaAs heterostructures include, but are not limited to,photovoltaics, nMOS MOSFETs, n-channel JFETs, NPN BJTs, MOS capacitors,and thin-film resistors (610, 620). More generally, an embodiment of thesubstrate with a NPN-junction in the silicon device layer additionallyenables pMOS MOSFETs, p-channel JFETs, and PNP BJTs, which arecomponents useful for more advanced CMOS devices. The above would not bepossible with standard CMOS manufacturing methods after the transfer ofAlGaAs heterostructures without damage to the AlGaAs heterostructures(630, 640).

Since the PN-junction, or PNP-junction is formed and dopants areactivated prior to the transfer of the AlGaAs heterostructures, theAlGaAs is not exposed to those elevated temperatures, addressing thesecond challenge discussed above.

FIG. 7A shows an example configuration including silicon MOSFETs,silicon photovoltaics, and AlGaAs LEDs fabricated on the substrate usingthe methods implemented based on some embodiments of the disclosedtechnology. Scale-bar in the upper-left corner is 100 microns. Theexample configuration also includes metal interconnects electricallyconnecting silicon MOSFETs, silicon photovoltaics, and AlGaAs LEDs toeach other and/or to other components not shown in FIG. 7A. In someembodiments of the disclosed technology, the metal interconnects can bephotolithographically formed such that the metal interconnects can havea smallest dimension under 10 microns and distances between electrodesare less than 40 microns. FIG. 7B shows optical image and performance ofmicron-scale of silicon nMOS MOSFET, FIG. 7C shows optical image andperformance of micron-scale of silicon photovoltaic, and FIG. 7D showsoptical image and performance of micron-scale of AlGaAs LED. Inperformance plots, uA is used as an abbreviation for microamps.

To address the remaining third challenge of releasing integrateddevices, this patent document presents a fabrication method that usesthe above substrate to produce wireless, optically powered inorganicoptoelectronics for cell-scaled sensors.

FIG. 8 shows example substrate and fabrication method schematics. At802, AlGaAs optical heterostructures transferred to the PN-junctioncontaining SOI wafer using the disclosed transfer method. At 804, thesilicon device layer is etched to various depths with inductivelycoupled plasma (ICP) based reactive ion etching using hydrogen bromide(HBr). This step forms the mesa structures for the silicon nMOS MOSFETsand photovoltaics. At 806, a thin dielectric is deposited using ALDserving as both an insulating layer and the gate dielectric. Thismaterial can be silicon dioxide, high-k dielectrics like hafnium oxide,or other desired dielectrics. At 808, metal contacts to the n- andp-type silicon are deposited (the oxide is removed in the contactopenings prior to deposition). The device is then annealed at 350degrees Celsius in argon to form ohmic contacts to the silicon. Othermetal or silicide contacts may be used as alternatives. At 810, gatemetal and metal interconnects are deposited. For example, a series oflayers including titanium (40 nanometers) and platinum (60 nanometers)are used as the gate metal. Other metals including, but not limited to,gold, chrome, aluminum, and copper may be used as alternatives. Othersemiconductor materials can be used for the gate including, but notlimited to, polysilicon and amorphous silicon.

At 812, openings in the BOX of the SOI wafer are etched using reactiveion etching. At 814, release tags are deposited. These tags, which canbe materials such as aluminum or photoresist, will serve to suspend thedevice and hold it in place until release of the devices is desired. At816, an SU8 photoresist layer is patterned to serve as an encapsulationlayer. Openings can be made to expose metal or other materials wheredesired, for sensing purposing or otherwise. Materials such as silicondioxide, parylene, or other insulators could be used as alternativeencapsulation layers. At 818, the silicon handle underneath the deviceis etched away using xenon difluoride (XeF2). This isotropic etch isvery selective for silicon over any of the other materials exposed(platinum, SU8, and silicon dioxide). In this step, the encapsulateddevice is suspended in air, held in place only by the small aluminumrelease tags. Other dry etches like SF6/O2 or wet etches such aspotassium hydroxide could be used as alternatives. At 820, the device isreleased in an etchant selective for the tags. In one embodiment withaluminum release tags, a dilute acid etch, such as hydrochloric acid(HCl) or another solution etchant, such as tetramethylammonium hydroxide(TMAH), can be used which selectively etches the aluminum release tagsbut does not etch the other exposed materials by any substantial amount.In another embodiment with exposed photoresist release tags, either adilute base or acetone can be used to release the devices withoutetching the other exposed materials. The solution can then be exchangedto deionized water then to any other desired solution.

FIGS. 9A-9D show example substrate and fabrication method schematicsillustrating a perspective view. FIG. 9A shows an AlGaAs LED formed on aSi substrate including n-type and p-type doped region with an SiO2 boxsurrounding the n-type and p-type doped region, and Si handle locatedunderneath the AlGaAs LED, n-type and p-type doped region and the SiO2box. FIG. 9B shows a Si MOSFET, an AlGaAs LED, Si photovoltaics disposedon a substrate. FIG. 9C shows an example without release tags, and FIG.9D shows another example with release tags. The disclosed substrate andfabrication method, allows for the massive, parallel release ofwireless, optically powered cell-scaled sensor or identificationdevices. The sensor and identification devices can be formed out of anydesired configuration of standard silicon electronics, AlGaAs opticalheterostructures, and other compatible materials, including, but notlimited to, 2D materials (graphene, MoS2, etc.), carbon nanotubes, andtransition metal dichalcogenides. In the section that follows, we detaildevices enabled by the above disclosure.

In light of the above, the disclosed technology can be implemented toprovide a device with opto-electronic circuitry to include a substrate;a photovoltaic module engaged to the substrate and structured to convertlight into electricity; and a sensor module engaged to the substrate andcoupled to receive power from the electricity generated by thephotovoltaic module, the sensor module structured to include a sensingelement that is responsive to a target substance to produce a response.The sensor module is further configured to generate, based on theresponse from the sensing element, an electrical sensor signalindicative of a property of the target substance. This device includes alight-emitting module engaged to the substrate and coupled to receivepower from the electricity generated by the photovoltaic module and toreceive the electrical sensor signal from the sensor module. Thelight-emitting module is structured to produce output light that ismodulated to carry the electrical sensor signal to wirelessly andoptically transmit the electrical sensor signal out of the device. Inimplementation, the sensing element can be in various configurations,including one or more sensing electrodes, one or more resistors such asa silicon resistor or a nanotube resistor, or other sensing elementdesigns.

The disclosed technology may be implemented to provide a method ofmaking lithographically-formed wireless sensors and devices, whereinintegration, packaging, and assembly is carried out in massive parallelthrough planar photolithography or electron beam lithography. Priormethods for making of wireless devices bulky or serial techniques for 1)integration of dissimilar materials, 2) device isolation, 3) packaging,and 4) assembly. Examples of these prior techniques that are notenabling of the disclosed technology include; wire-bonding, flip-chipbonding, solder bumps, dicing, dice-before-grind, pick-and-place,stacking, and dip coating for encapsulation. Unlike such prior methods,the methods disclosed in this document enable the making of a devicecomprising a (i) light emitting element module, (ii) a photovoltaicmodule, and (iii) a sensing or identification module, wherein allcomponents have lithographically-formed electrical interconnects.Additionally, the methods enable the parallel production of devicescomprising a (i) light emitting element module, (ii) a photovoltaicmodule, and (iii) a sensing or identification module.

Based on the disclosed technology, the photolithographic or e-beamlithographic formation of electrical contacts allows for size scales anddimensions of electrical interconnects that would otherwise beunattainable. In some embodiments, the wireless optoelectronic devicesenabled could have electrical interconnects with one dimension at orbelow 40 microns, 30 microns, 20 microns, 15 microns, 10 microns, 5microns, 3 microns, or 1 micron. In other embodiments, the pitch betweenelectrical interconnects connecting dissimilar materials could be at orbelow 40 microns, 30 microns, 20 microns, 10 microns, 5 microns, or 3microns.

Based on the disclosed technology, the use of all planar techniques for(i) lithographic integration, (ii) interconnects, (iii) assembly, (iii)packaging, and (iv) release of the devices from the substrate on whichthey were built, allows for size scales and dimensions of thefully-integrated, stand-alone device that would otherwise beunattainable. In some embodiments, the wireless optoelectronic devicesenabled could have dimensions below 1 mm³, (500 μm)³, (400 μm)³, (300μm)³, (200 μm)³, or (100 μm)³.

Based on the disclosed technology, sensing a target subject byimplanting a sensor on the target subject without having a physicalconnection to the sensor can be achieved. In this method; illuminationlight is directed onto the sensor implanted on the target subject tocause a photovoltaic module in the sensor generate electric power foroperating the sensor so that the generated electric power powers (1) asensor module which performs a sensing operation on the target subjectto generate an electrical sensor signal indicative of a property of thetarget subject, and (2) a light-emitting module coupled to receive theelectrical sensor signal from the sensor module and operable to produceoutput light that is modulated to carry the electrical sensor signal.The output light is used to wirelessly and optically transmit theelectrical sensor signal out of the device.

In another embodiment of the disclosed technology, a device withopto-electronic circuitry includes a substrate, a photovoltaic moduleengaged to the substrate and structured to convert light intoelectricity, an identification module engaged to the substrate andcoupled to receive power from the electricity generated by thephotovoltaic module, the identification module configured to generate anelectrical identification signal indicative of an identity of thedevice, and a light-emitting module engaged to the substrate and coupledto receive power from the electricity generated by the photovoltaicmodule and to receive the electrical identification signal from theidentification module, the light-emitting module structured to produceoutput light that is modulated to carry the electrical identificationsignal to wirelessly and optically transmit the electricalidentification signal out of the device.

In some embodiments of the disclosed technology, the output light can bemodulated using a pulsed-position modulation scheme. For example, thesignal measured from the sensor module or the identification module isencoded in the timing between pulses.

Examples of Wireless, Self-Powered Sensor Devices

FIGS. 10A-10D show examples of large-scale integration of micron-scalesilicon and III-V electronics and optoelectronics for releasabledevices. Specifically, FIG. 10A shows an optical image of an 18 by18-millimeter chip where thousands of GaAs micro-LEDs have beentransferred to a silicon-on-insulator substrate with a PN-junctionformed in the silicon handle. Silicon electronics were then fabricatedaligned to the GaAs micro-LEDs. An example die on the chip is shown inFIG. 10B after transfer of GaAs LEDs, but before silicon electronics arefabricated. FIG. 10C shows an example die after silicon electronics havebeen integrated. Devices shown in FIG. 10D includes micron-scale voltagesensors that are optically powered with silicon photovoltaics and areoptically readout with GaAs micro-LEDs.

Using the above disclosed transfer method, substrate, and fabricationmethods, we regularly produce optoelectronic integrated circuits (ICs)that are capable of being released from the silicon handle. FIG. 10Ashows an example on an 18 millimeter chip where AlGaAs micro-LEDs andsilicon electronics have been integrated, including optically powered,cell-scale sensor and identification systems. On such a chip, there areabout 50 different IC designs and thousands of individual ICs. In someembodiments of the disclosed technology, the AlGaAs micro-LEDs andsilicon electronics integrated on the chip are electrically connected toeach other through metal interconnects that are photolithographicallyformed such that the metal interconnects can have a smallest dimensionunder 10 microns and distances between electrodes of the AlGaAsmicro-LEDs are less than 40 microns.

FIGS. 11A-11F show an example integrated circuit of GaAs LED and siliconMOSFET. Specifically, FIG. 11A shows a circuit schematic of integrateddevice with a GaAs LED in series with a Si MOSFET. FIG. 11B shows anoptical image taken with a CCD camera, capable of monitoringnear-infrared light, of the integrated LED/MOSFET system under nogate-source bias. The silicon MOSFET shown, as well as all other siliconelectronics shown in the image, was fabricated after transfer of theGaAs LED. FIG. 11C shows an optical image of the same device with apositive gate-source bias applied showing light being emitted from theLED. FIG. 11D shows optical images 1102, 1104, 1106 taken at highermagnification of the integrated device in order of increasinggate-source bias from 1102 to 1106. For scale, channel length of thesilicon MOSFET is approximately 2 microns. FIGS. 11E and 11F showperformance of the integrated LED/MOSFET system. As one example of theintegration of AlGaAs micro-LEDs and silicon electronics, FIGS. 11A-11Fshow optical images and data from a AlGaAs LED and a silicon nMOS MOSFETconnected in series. The electric signal input into the gate of theMOSFET is converted into an optical signal out of the micro-LED that canbe readout using a CCD camera or other photodetector.

FIGS. 12A-12F show examples of optically powered voltage sensorfabrication on a release-compatible substrate. Specifically, FIG. 12Ashows a circuit schematic of the optically powered, wireless,cell-scaled voltage sensor. FIG. 12B shows an optical image of device ona release-compatible substrate. FIG. 12C shows a power output of themicro-LED as a function of gate voltage. The device is under 25nanowatts per micron squared illumination, providing the power to thecircuit. FIGS. 12D-12E show power outputs of the micro-LED and inputvoltage signal for different input voltage pulses. These plotsillustrate the conversion of the input electrical signal to an opticalsignal out. FIG. 12F shows an example measurement setup for powering andmonitoring the optically powered, voltage sensor.

The voltage sensor implemented based on some embodiments of thedisclosed technology may include silicon photovoltaics, a siliconMOSFET, and a AlGaAs micro-LED. In an implementation, the approximately50-micron by 200-micron voltage sensor is capable of detecting changesin voltage in its surroundings and then communicating out those changesoptically using the integrated micro-LED. In this embodiment, the signalis encoded in changes in intensity of the LED. More complex embodimentscan have additional features to reduce noise and encode the outputsignal using other encoding schemes as shown in FIGS. 5A-5F where thevoltage sensor is sensitive to approximately 10 nanovolts/Hz1/2 and thesignal is communicated out through pulse position modulation. Bothwireless, optically powered, cell-scale sensors could be used forapplications such as recording neural activities at the individual celllevel.

FIGS. 13A-13E show example wireless, optically powered, cell-scalesensor systems and applications. Specifically, FIG. 13A shows schematicof a wireless, optically-powered cell-scale sensor system under use. Thesame techniques used to produce the voltage sensor described above canenable various embodiments of wireless, optically-powered cell-scalesensor systems. A general schematic of such a sensor system is shown inFIG. 13A. Optical power, λ1, is supplied to the system along with anyoptical communication in, λ2. Using the power supplied and anycommunication in, the cell-scaled sensor system can apply a signal ifdesired. Signal in from the sensor system environment is thencommunicated out optically, λ3. The sensor systems can make using ofvoltage sources, current sources, sensors that measure voltages, andsensors that measure currents.

FIGS. 13B-13E detail example wireless, optically-powered, cell-scaledsensor system embodiments and applications enabled by the presentdisclosure. FIG. 13B shows, as an example application for a voltagesensor, a device capable of measuring the electrical signals from anindividual neuron, including schematics of (b.i) circuit, (b.ii) exampleapplication of detecting neuron activity, and (b.iii) signal inreconstructed from λ3. FIG. 13C shows, as an example application for acurrent sensor with voltage source controlled with λ2, a device capableof performing and measuring cyclic-voltammetry in a small volume offluid to, for example, determine the presence of dopamine released froma cell including schematics of (c.i) circuit, (c.ii) example applicationof performing cyclic-voltammetry, and (c.iii) cyclic voltammogramreconstructed from λ3. FIG. 13D shows, as an example application for agraphene sensor with voltage source controlled with λ2, a device capableof measuring the response of graphene or carbon nanotubes to thepresence of DNA, including schematics of (d.i) circuit, (d.ii) exampleapplication of detection DNA, and (d.iii) signal in reconstructed fromλ3. FIG. 13E shows, as an example application for a silicon sensor withvoltage source controlled with λ2, a device capable of measuring theresponse of a silicon resistor to changes in temperature allowing formonitoring of flow and turbulence in fluids, including schematics of(e.i) circuit, (e.ii) example application of detection of fluid flow ortemperature change, and (e.iii) signal in reconstructed from λ3.

The disclosed technology in this patent document can be used formonitoring electrical and chemical signals at the cellular-scale.Examples of the monitoring method can include monitoring electricalsignals from neurons, nerve cells, cardiomyocytes, and other biologicalsystems. In some implementations, many devices in parallel may be usedfor brain mapping of neural activity. Examples of the monitoring methodalso include monitoring chemical signals or chemical composition of, ornear, cells or other biological systems. Here, many devices in parallelmay be used for mapping of chemical release in the brain (or mappingchanges in chemical composition). Examples of the monitoring methodinclude the chemical detection of glucose levels, oxygen content, A1Ctesting, PH, pregnancy, infectious disease, and drug-of-abuse. Examplesof the monitoring method include monitoring changes in electricalsignals from nanoscale materials (metal electrodes, tunnel junctions,carbon nanotubes, graphene, other 2D materials, etc.) that are sensitiveto particular chemical species in solution. Examples of the monitoringmethod also include monitoring electrical signals, chemical signals,temperature, or flow in nanoscale or microscale fluid channels. Manydevices in parallel could be used for mapping flow, turbulence, orsolution conductivity in microfluidic channels. Examples of themonitoring method include the transfer method may be used to makemicro-shanks with integrated AlGaAs LEDs for optogenetics.

Example of Alternative Methods Used in Fabrication

FIG. 14 shows an example alternative release method for integrated CMOSand AlGaAs heterostructure cell-scale sensors. At 1402, AlGaAs opticalheterostructure is transferred and adhered to CMOS circuitry using thedisclosed methods. At 1404, metal interconnects are patterned toelectrically connect the anode and cathode of the AlGaAs opticalheterostructure to the corresponding connections of the CMOS circuitthrough the CMOS inputs. At 1406 dual chrome and alumina masking layersare deposited and patterned to protect the circuitry and opticalheterostructure during etches through the CMOS dielectric layers and theunderlying bulk silicon substrate. Other masking layers can be used aslong as they are selective enough for the subsequent etches. Other suchcombinations can include combinations of photoresist, alumina, tantalumoxide, titanium dioxide, chrome, and nickel. At 1408, reactive-ionetching (RIE) through the CMOS dielectric is used to etch the desiredsize and shape of the released, cell-scale device. An example RIEchemistry suitable for such etching is inductively coupled plasma RIEconsisting of CHF₃ and O₂. At 1410, the chrome is selectively removed inchrome etchant and the remaining alumina is used to mask the circuitryand the optical heterostructure during deep reactive ion etching (DRIE)into the silicon. The etch depth into the silicon is used to determinethe eventual thickness of the singulated device or die. At 1412, thealumina is selectively removed in, e.g., a BCl₃ RIE chemistry, and aconformal encapsulation layer coats the device and is then opened at thedesired inputs of the CMOS circuitry. SU8, parylene, silicon dioxide,and other insulating materials can be used as an encapsulation layer. At1416, for both protection and adhesion, the device is bonded,device-side down to a transfer substrate. The adhesion/protection layeris chosen so that it can be selectively etched with respect to the otherexposed materials. Examples of the materials that could be used for thislayer include, but are not limited to, photoresist, PMMA, and dicing sawtape. A silicon, sapphire, or other substrate could be used for thetransfer substrate. At 1416, deep reactive-ion etching (DRIE) or wafergrinding is used to etch down to the desired device thickness. At thispoint the device is only held to the transfer substrate via theadhesion/protection layer. At 1418, the device can then be release byusing a wet or dry etches selective for the adhesion/protection layer.

In one embodiment, UV dicing saw tape can be used for theadhesion/protection layer. The device can then be released by floodexposing the tape to UV light.

In one embodiment, silicon dioxide can be used as the encapsulationlayer, photoresist can be used as the adhesion/protection layer, and therelease of the device can be accomplished using an acetone solution.This alternative method enables the release of cell-scale devices fromboth SOI substrates or standard CMOS substrates.

The examples of fabrication methods described represent a novel methodfor singulation of dies or devices over some other dicing methods. Someimplementations of those other dicing techniques for die singulationtend to be limited in one or more aspects, including, for example: (1)dicing may not be a fully parallel process, (2) the thickness of thedicing saw may dictate the smallest size of the trench or cut made, and(3) the available shapes may be geometrically limited by the size anddirection of the blade. The above methods do not suffer from any ofthese limitations. With respect to (1), the processes listed above canbe achieved fully in parallel through planar lithographic methods. Afull wafer can be processed in a single process, reducing time and costof singulation. With respect to (2), the thickness of the etch is onlylimited by lithography and the aspect ratios possible with the RIEtechniques used. Trenches with dimensions at or below 40 microns, 30microns, 20 microns, 10 microns, 5 microns, 2 microns, and 1 micron areattainable using the disclosed methods. With respect to (3) thegeometric shapes are only limited to what shapes can be lithographicallyproduced on the substrates. Each individual die can have its ownarbitrary shape on the same wafer.

Although methods disclosed here can be used for wireless optoelectronicdevice singulation, these methods may also be used for singulation ofCMOS or other semiconductor dies with much less space etched betweendevices, or kerf, lost during process. Size scales of kerf possible withthe disclosed techniques represent a departure from what is achievablethrough prior techniques. For example, on a CMOS process, if dies are tobe singulated into 200 μm dies using a dicing saw with 40 micronthickness, approximately 40 percent of the wafer would be lost todicing. In comparison, if dies are to be singulated into 200 μm diesusing 2 micron trenches as achievable with the disclosed methods, onlyapproximately 2 percent of the wafer would be lost during singulation.

Additional Sensor Examples

FIGS. 15A-15D illustrate examples of sensors made by using large-scaleintegration of micron-scale silicon and III-V electronic andoptoelectronics for releasable devices. Specifically, FIG. 15A shows atemperature sensor having silicon photovoltaics and AlGaAs micro-LED.FIG. 15B shows sample characteristics of the temperature sensing of thetemperature sensor in FIG. 15A showing a linear optical response as afunction of temperature (top), a circuit schematic of the temperaturesensor (insert) and high-speed temperature sensing of pulsing heatingusing a resistive element next to the temperature sensor (bottom). FIG.15C shows a voltage sensor having silicon photovoltaics, a siliconMOSFET, AlGaAs micro-LED, and input electrodes. FIG. 15D shows samplevoltage sensor characteristics represented by the power output as afunction of input voltage of the sensor in FIG. 15C (top) and high-speedvoltage sensing data from the optical voltage sensor (bottom). Devicesshown here are capable of release from the substrate and encapsulated.Interconnects for the GaAs micro-LEDs were made using photolithographyas opposed to wire-bond or flip-chip methods.

FIGS. 16A-16G show examples of wireless, optically poweredoptoelectronic cell-scale sensors. Specifically, FIG. 16A shows 18 mm by18 mm chips containing thousands of releasable wireless,optically-powered optoelectronic cell-sized sensors that were integratedwith photolithographically defined interconnects. FIG. 16B shows anexample die showing the release structure of the devices. FIG. 16C showsoptically powered, wireless optoelectronic voltage and temperaturesensors that are suspended over a trench as described in the abovematerials. FIG. 16D shows wireless devices released into solution byselective chemical etching of the release tags. FIG. 16E shows releasedwireless optically powered optoelectronic device next to cardiac cells.FIG. 16F shows released wireless optically powered optoelectronic deviceon a ridge of a human finger. FIG. 16G shows wireless optically poweredoptoelectronic temperature sensors implanted in-vivo to a mouse's brain.

The above and other technical features as disclosed can be used toconstruct optically powered, wireless sensors at small scales of 10,000times smaller in volume than some mm-scale sensors by integratingoptical components (such as light-emitting diodes) with interconnectsthat are photolithographically defined while avoiding bulky wire-bond orflip-chip bonding for forming interconnects of greater than 40 um pitch.By using photolithographically defined interconnects, the disclosedtechnology in this document can be used achieve smaller sizeintegration, e.g., with all electrical interconnect having a dimensionless than 10 microns.

In some example applications, a method of transferring AlGaAs systemheterostructures may include: producing AlGaAs system heterostructureson a substrate with an “intermediate selective etch layer” betweenheterostructures and the substrate; depositing a layer of polymer on theoptical heterostructures; etching the substrate in a chemical mixture(citric acid and hydrogen peroxide); etching the intermediate selectiveetch layer in a distinct chemical mixture (diluted HF); transferring thepolymer/optical heterostructure system to a transfer substrate. In anembodiment, a method of transferring AlGaAs system heterostructures mayinclude removing the polymer via a dry etching method; adhering thedevices to the transfer substrate by deposition a conformal insulatingmaterial (ALD, PECVD, etc.). In an alternative embodiment, a method oftransferring AlGaAs system heterostructures may include: producingAlGaAs system optical heterostructures on a substrate with an“intermediate selective etch layer” between optical heterostructures andthe substrate; depositing a layer of polymer on the opticalheterostructures, etching the intermediate selective etch layer in adistinct chemical mixture (diluted HF); and transferring thepolymer/optical heterostructure system to a transfer substrate.

As an example substrate implemented based on some embodiments of thedisclosed technology, a substrate for the integration of siliconelectronics and AlGaAs system optical heterostructures may include: anoptical heterostructure transferred to a silicon-on-insulator substratewith; a silicon handle with thickness less than 100 microns. Apn-junction has been formed in the silicon handle with dopantsactivated; the silicon device layer has been etched; electrical contacthas been made to at least one area of n-type silicon; and electricalcontact has been made to at least one area of p-type silicon.

As an example device implemented based on some embodiments of thedisclosed technology, an electronic and optical device may include: asubstrate; and a device comprising; at least one micron-scale AlGaAssystem optical heterostructure; at least one transistor; at least onephotovoltaic. The three components are connected with electricalinterconnects in a configuration such that under illumination ofelectromagnetic radiation, electric current passes through the threecomponents, changes in voltage or current in connections made to thetransistor result in modulations in current passing through the AlGaAsoptical heterostructure, and modulation of said electric current causeschanges in the amount of the light emitted from the AlGaAs systemoptical heterostructure. All dimensions of the components of the deviceis less than 1000 microns.

In the disclosed examples, “wireless” is used to describe a device thatdoes not have electrical interconnects emanating from the device. Theelectrical interconnects are internal to the device. If a device is saidto be a wireless with all dimensions less than 100 microns, there are noelectrical interconnects extending outside of the 100 micron boundarybounding the device. “cell-scaled,” “cellular-scale,” and “cell-sized”are used interchangeably to describe an object that has all dimensionsless than 500 microns on every side. The term “micro-LED” is used todescribe a light-emitting diode that has all dimensions less than 1millimeter on every side. The term “heterostructure” is used to describeany series of layers of materials grown on a substrate to produce anoptical or electronic device. The term “optical heterostructure” is usedto describe structures or layers of materials grown on a substrate thathave the capability to emitting or absorbing light. This would includelight-emitting diodes, lasers, photovoltaics, as well as other opticalelements. The terms “AlGaAs material system,” “AlGaAs system,” “AlGaAs,”

“AlGaAs/GaAs,” and “AlGaAs/GaAs system” are used interchangeably todescribe any material or layers of materials that are sufficientlylattice-matched to GaAs to allow for optical heterostructures to beproduced. This would include material systems such as GaAs, AlGaAs,AlGaInP, GaAsP, AlInP, and/or GaP which can all be grown on the samesubstrate to produce optical heterostructures. The term “AlGaAsheterostructure” is used to describe a heterostructure or opticalheterostructure made of materials from the AlGaAs system. “Fabrication,”“micro-fabrication,” and “nano-fabrication” are used interchangeably todescribe fabrication or production of devices at the nanometer tomillimeter scale. “Light” and “electromagnetic radiation” are usedinterchangeably. “BJT” is an abbreviation for bipolar junctiontransistor. “JFET” is an abbreviation for junction gate field-effecttransistor.

In some embodiments of the disclosed technology, the photovoltaicprovides power, the silicon circuitry measures, amplifies, and encodesthe signal, and finally, the signal is optically communicated out usingthe LED functionality of the PVLED.

FIGS. 17A-17B show a block diagram of the system and a schematic of theamplifier that boosts the differential signal between the two sensingelectrodes that are spaced ˜150 μm apart to sample the electric fieldsgenerated by nearby neurons. Specifically, FIG. 17A shows a blockdiagram of the system implemented based on some embodiments of thedisclosed technology. FIG. 17B shows schematic of an amplifier includinga startup circuit and a filtering circuit. Approximately one half of thetotal current from the PVLED (500 nA of 1 μA) is used to provide the lownoise amplification through the input differential pair (M1 & M2). Apair of NFETs (M3 & M4) act as high-pass active loads: the amplifieroutput is fed back to the gates from through transistors acting aspseudo resistors and shunted by MOS capacitors. Thus, M3 and M4 providea low impedance at low frequencies (<<1 Hz) but a high resistance in theneural band of interest (>10 Hz). Finally, a pair of diode-connectedPFETs (M5 & M6) provide a matched load for a controlled mid-band gain,with parallel MOS capacitors setting a low-pass corner at about 10 KHzto suppress higher-order aliasing terms. Because the high-pass loadwould lead to a prohibitively long start-up time while illumination maybe transitory, the high-pass resistors are briefly set to a lowresistance state at VDD startup, to rapidly calibrate out DC offsets andbias state before switching to their normal high-resistance state. Theamplifier and all other circuits are biased from a supply-invariantPTAT-like current source to provide immunity to variations in VDD duringillumination fluctuation or output optical pulse generation.

Some embodiments of the disclosed technology can use a pulse positionmodulation (PPM) for signal encoding for its high information per photonefficiency. FIGS. 18A-18D show that the amplifier drives thepulse-position encoder, while a 10 KHz relaxation oscillator generates aperiodic pulse, which charges capacitor C1 to VDD. Specifically, FIGS.18A and 18B show the PPM encoder and associated timing diagram, andFIGS. 18C and 18D show the pulse generator and its associated timingdiagram. After this reset, the capacitor is discharged by one of twodifferential currents generated from the output of the amplifier. Theresult is a square-wave whose duty cycle reflects the inverse of themeasured voltage. Fixed currents bound the duty cycle to a range between20% and 80%. A T-flip-flop selects which of the two complementarycurrents discharges the capacitor, alternating between clock cycles,chopping like this allows separation of signal from fluctuations due toslow-changing light level. The resulting square-wave is passed through adelay-line of current-starved inverters, and edges are combined togenerate pulses on both the rising and falling edges of the square wave.The timing of these signals is illustrated in FIGS. 18B and 18D. A widerpulse disconnects VDD from the PVLED for 1 μs, and two other pulsesswitch a 3-capacitor (1.2 pF each) charge pump, switching from aparallel configuration to a series configuration, and connecting to thePVLED to deliver a sharp (<100 ns) current pulse. Each cycle of therelaxation oscillator generates two light pulses through the PVLED, oneat the beginning of the cycle, and the other between 20 μs and 80 μslater, where this time difference denotes the input voltage. To ensurethat the VDD does not drop excessively during the pulsing events (whenit is disconnected from the PVLED), 16 pF of decoupling capacitance isinstalled. In addition, because the PVLED can only supply a finiteamount of instantaneous current, and to avoid an excessive supplyripple, the charge pump capacitors are recharged slowly over about 10μs. A 20 μs minimum pulse spacing ensures that the charge pump is fullycharged before each pulse. Finally, to ease the assembly of PVLED andCMOS, a cross-coupled rectifier (polarity corrector) is implemented toensure the system functionality regardless of the polarity of the PVLEDon its pads.

FIGS. 19A-19B show example measurement of optical output pulse (FIG.19A), and associated reconstructed 1 KHz waveform (FIG. 19B). FIGS.19C-19D show signal gain as a function of frequency (FIG. 19C) andamplitude (FIG. 19D). The CMOS circuit is fabricated in 180 nm CMOS,with an active area of 210 μm×90 μm. For testing, the CMOS may be bondedto a PVLED. When illuminated with about 50 nW/μm2 of band-passed whitelight (380 nm-720 nm), which is about ⅙th of the safe limit for braintissue, light pulses are measured as expected as shown in FIG. 19A.Driving the input electrodes with voltage signals modulates the timingof the pulses, from which the input is successfully reconstructed asshown here for a 1 KHz test signal. The system has a transduction gainof 140 ns/μV across 1 Hz-10 KHz and the gain compresses for largerinputs>3 mVPP (1.1VRMS) whereas the input referred noise floor of isabout 21 μVRMS. The wake-up characteristics of the system for itspotential use in pulse-powered environment (as opposed to continuousexposure as shown in FIG. 5A) may allow the system to wake up in under 1ms.

FIG. 19A also shows an example of the device communicating near 20 kHz,but at a specific frequency that can be precisely measured to manydecimal places, e.g. 19,857.12 Hz. This information provides theidentity of the individual sensor. Small manufacturing differencesbetween devices results in slightly different clock cycles. Hence anexample device operating with a clock cycle of 19,857.12 Hz can bedistinguished from a device with a 18,354.47 Hz clock cycle. Thisfeature of the system imbues the device with a unique identitycommunicated optically and wirelessly.

FIG. 28 shows one embodiment of a fully-integrated, stand-alone wirelessoptical device configured to generate a predetermined electricalidentification signal indicative of an identity of the device. Aphotovoltaic module is configured to power the identification modulewith a supply voltage VDD. This power turns on a relaxation oscillator(e.g., a clock generator labeled CLOCK) which provides a periodic pulseto serve as the clock of the circuit. A set of counters, e.g. ringcounter, labeled X COUNTER and Y COUNTER, provide an electric signal toa set of decoders, labeled X DECODER and Y DECODER, which are fed into amemory element (e.g., a memory labeled MEMORY). The output of the memoryelement is a sequence of voltages at either a low voltage, ground, or ahigh voltage VDD. The output of the memory element is configured tomodulate the output light of the light emitting module, to carry theelectrical identification signal to wirelessly and optically transmitthe electrical identification signal out of the device. In oneembodiment the timing of the output pulses of light from the lightemitting module transmit the identity of the device. In anotherembodiment the sequence of light pulses from the light emitting module,labeled LIGHT EMITTING MODULE, transmits the identity of the device. Theidentification module is further configured to have a counter and reset(e.g., functional block labeled COUNTER AND RESET) which resets thememory of device, discharging any memory elements.

FIGS. 20A-20B show start-up, showing onset of optical pulses (FIG. 20A)and decoded signal (FIG. 20B). FIGS. 20C-20S show neural recording on anearthworm ventral nerve upon mechanical stimulation measured in parallelthrough a commercial amplifier to provide baseline (FIG. 20C) and usingthe presented system, powered and communicating optically (FIG. 20D). Todemonstrate the system's capability to encode real neural signals, theinput electrodes may be connected to the ventral nerve cord of anearthworm using probes, with a commercial neural amplifier connected inparallel to provide a reference baseline. FIGS. 20C-20S clearly showthat the composite spikes have been accurately encoded in the outputoptical pulses, even when communication and power are purely optical.

FIG. 21 shows a breakdown of the design by power consumption (top-left)and by Si area (top-right). As emphasized earlier, the power consumptionis dominated by the main amplifier and the charge pump. Area isdominated by the amplifier (for lower flicker noise), LED driver, anddecoupling. The bottom of the FIG. 6 shows a table of comparison againstprior art.

FIG. 22 shows an example of the optical wireless integrated circuitsensor implemented based on some embodiments of the disclosedtechnology. As discussed above, such optical wireless integrated circuitsensors can be used for implantable medical diagnostics for neuralactivity, temperature monitoring for cancer cell growth or others.Various embodiments of the disclosed technology can be used to implementsystems monitoring in micron-scale systems or materials, such asmicrofluidics, lab-on-a-chip, thermal properties of small samplesmaterials.

FIG. 23 shows an example of the optical wireless sensor device 2300implemented based on some embodiments of the disclosed technology. Theoptical wireless sensor device 2300 may include a photovoltaic module2302, a sensor module 2304, and a light-emitting module 2306. Thephotovoltaic module 2302 is structured to convert light L1 intoelectricity. The sensor module 2304 is coupled to photovoltaic module2302 to receive power from the electricity generated by the photovoltaicmodule 2302. The sensor module 2304 is structured to include a sensingelement that is responsive to a target substance 2310 to produce aresponse. The sensor module 2304 may also generate, based on theresponse from the sensing element, an electrical sensor signalindicative of a property of the target substance 2310. Thelight-emitting module 2306 is coupled to receive power from theelectricity generated by the photovoltaic module 2302 and to receive theelectrical sensor signal from the sensor module 2304. The light-emittingmodule 2306 may also produce output light L2 that is modulated to carrythe electrical sensor signal to wirelessly and optically transmit theelectrical sensor signal out of the device.

FIG. 24 shows an example of the optical wireless sensor device 2400implemented based on some embodiments of the disclosed technology. Theoptical wireless sensor device 2400 includes a photovoltaic module 2402structured to convert electromagnetic radiation L1 and L2 intoelectricity. The optical wireless integrated circuit sensor 2400 alsoincludes a sensor module 2404 coupled to the photovoltaic to receive theelectricity generated by the photovoltaic module. The sensor module 2404includes a sensing element 2406 and a communication element 2405. Thesensing element 2406 is responsive to a target substance 2410 to producea response, and the communication element 2405 is structured togenerate, based on the response from the sensing element 2406, anelectrical sensor signal indicative of a property of the targetsubstance 2410. The optical wireless sensor device 2400 also includes alight-emitting module 2408 coupled to the photovoltaic module 2402 toreceive the electricity and coupled to the communication element 2305 ofthe sensor module 2404 to receive the electrical sensor signal andconvert the electrical sensor signal to output electromagnetic radiationL3 indicative of the property of the target substance 2410. Theelectricity generated by the photovoltaic module is used to supply powerto the sensor module 2404 and the light-emitting module 2408. In anembodiment of the disclosed technology, the electricity generated by thephotovoltaic module may also be used to generate electrical controlsignals for controlling the sensor module 2404 and the light-emittingmodule 2408. In an embodiment of the disclosed technology, the radiationL1 is converted into power for operating the sensor module 2404 and thelight-emitting module 2408, and the radiation L2 is converted intoinformation associated with operations of the sensor module 2404 and/orthe light-emitting module 2408 such as instructions for controlling thesensor module 2404 and/or the light-emitting module 2408. Here, theoptical wavelength of the radiation L2 may be different from that of theradiation L1.

FIG. 25 shows an example of the optical wireless identification device2500 implemented based on some embodiments of the disclosed technology.The optical wireless identification device 2500 may include aphotovoltaic module 2502, an identification module 2504, and alight-emitting module 2506. The photovoltaic module 2502 is structuredto convert light L1 into electricity. The identification module 2504 iscoupled to photovoltaic module 2502 to receive power from theelectricity generated by the photovoltaic module 2502. Theidentification module 2504 configured to generate an electricalidentification signal indicative of an identity of the device. Thelight-emitting module 2506 may also produce output light L2 that ismodulated to carry the electrical identification signal to wirelesslyand optically transmit the electrical identification signal out of thedevice.

FIG. 26 shows an example of pulsed-position modulation (PPM) encodingwhere V_(PD) and Δt denotes photodetector output and pulse spacing(between the primary and secondary), respectively. In some embodimentsof the disclosed technology, the output light can be modulated using apulsed-position modulation scheme. For example, the signal measured fromthe sensor module or the identification module is encoded in the timingbetween pulses as shown in FIG. 26. One set of pulses, “primary peak.”occurs at some regular frequency. Another set of pulses (every otherpulse), “secondary peak,” encodes the input signal. In thisimplementation, the time between pulses encodes the voltage. In thisway, the output light can be modulated to carry the electrical sensorsignal or the electrical identification signal to wirelessly andoptically transmit the electrical sensor signal out of the device.

FIG. 27 shows an example method for sensing a target subject. The methodincludes, at 2702, implanting a sensor on a target subject withouthaving a physical connection to the sensor, at 2704, directingillumination light onto the sensor implanted on the target subject tocause a photovoltaic module in the sensor to generate electric power foroperating the sensor so that the generated electric power powers (1) asensor module which performs a sensing operation on the target subjectto generate an electrical sensor signal indicative of a property of thetarget subject, and (2) a light-emitting module coupled to receive theelectrical sensor signal from the sensor module and operable to produceoutput light that is modulated to carry the electrical sensor signal,and, at 2706, receiving information indicative of the property of thetarget subject by using the output light to wirelessly and opticallytransmit the electrical sensor signal out of the device.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this patent document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

1. A device with opto-electronic circuitry, comprising: a substrate; aphotovoltaic module engaged to the substrate and structured to convertinput light into electricity; a sensor module engaged to the substrateand coupled to receive power from the electricity generated by thephotovoltaic module, the sensor module structured to include a sensingelement that is responsive to a target substance to produce a response,wherein the sensor module is further configured to generate, based onthe response from the sensing element, an electrical sensor signalindicative of a property of the target substance; and a light-emittingmodule engaged to the substrate and coupled to receive power from theelectricity generated by the photovoltaic module and to receive theelectrical sensor signal from the sensor module, the light-emittingmodule structured to produce output light that is modulated to carry theelectrical sensor signal to wirelessly and optically transmit theelectrical sensor signal out of the device.
 2. The device as in claim 1,further comprising one or more electrical interconnects configured toelectrically connect the light-emitting module to the photovoltaicmodule and the sensor module, wherein the one or more electricalinterconnects have a dimension less than 10 microns.
 3. The device as inclaim 1, wherein the device with opto-electronic circuitry is structuredto have a volume less than 1 mm³.
 4. The device as in claim 1, furthercomprising an identification module engaged to the substrate and coupledto receive power from the electricity generated by the photovoltaicmodule, wherein the identification module is configured to generate anelectrical identification signal indicative of an identity of thedevice, and wherein the light-emitting module is configured to produceoutput light that is modulated to carry the electrical identificationsignal to wirelessly and optically transmit the electricalidentification signal out of the device.
 5. The device as in claim 4,wherein the output light is modulated using a pulsed-position modulation(PPM) encoding scheme.
 6. The device as in claim 4, wherein the deviceis configured to output only the output light modulated to carry theelectrical identification signal upon receipt of a predetermined inputlight. 7-10. (canceled)
 11. The device as in claim 1, wherein: thesensor module is structured to generate the electrical sensor signalindicative of a temperature of the target substance.
 12. The device asin claim 1, wherein: the sensor module is structured to generate theelectrical sensor signal indicative of a biological substance or achemical substance in the target substance or an electrical property ofthe target substance or any two or more of the biological substance inthe target substance, the chemical substance in the target substance,and the electrical property of the target substance with or withoutothers.
 13. The device as in claim 1, wherein: the sensing elementincludes a sensing electrode, and the sensor module is structured togenerate the electrical sensor signal from interacting with one or moreneurons as the target substance via the sensing electrode. 14-18.(canceled)
 19. A device with opto-electronic circuitry, comprising: asubstrate; a photovoltaic module engaged to the substrate and structuredto convert light into electricity; an identification module engaged tothe substrate and coupled to receive power from the electricitygenerated by the photovoltaic module, the identification moduleconfigured to generate an electrical identification signal indicative ofan identity of the device; and a light-emitting module engaged to thesubstrate and coupled to receive power from the electricity generated bythe photovoltaic module and to receive the electrical identificationsignal from the identification module, the light-emitting modulestructured to produce output light that is modulated to carry theelectrical identification signal to wirelessly and optically transmitthe electrical identification signal out of the device.
 20. The deviceas in claim 19, further comprising one or more electrical interconnectsconfigured to electrically connect the light-emitting module to thephotovoltaic module and the identification module, wherein the one ormore electrical interconnects have a dimension less than 10 microns. 21.The device as in claim 19, wherein the device with opto-electroniccircuitry has a volume less than 1 mm³.
 22. The device as in claim 19,wherein the device is configured to output the light modulated to carrythe electrical identification signal upon receipt of a predeterminedinput light. 23-25. (canceled)
 36. A method for constructing a devicewith opto-electronic circuitry, comprising: forming a semiconductorrelease layer over a first semiconductor substrate; fabricatingphotoelectronic semiconductor structures over the semiconductor releaselayer; forming a polymer layer over the fabricated photoelectronicsemiconductor structures over the semiconductor release layer to embedthe fabricated photoelectronic semiconductor structures in the formedpolymer layer; performing an etching process to remove the semiconductorrelease layer from the polymer layer and the fabricated photoelectronicsemiconductor structures that are embedded in the polymer layer so thatthe polymer layer and the fabricated photoelectronic semiconductorstructures that are embedded in the polymer layer become an isolatedassembly; and transferring the polymer layer and the fabricatedphotoelectronic semiconductor structures that are embedded in thepolymer layer to a second semiconductor substrate.
 37. The method as inclaim 36, further comprising, before performing the etching process toremove the semiconductor release layer, forming a release layer to acarrier substrate to hold the fabricated photoelectronic semiconductorstructures temporarily after the semiconductor release layer is etched.38-40. (canceled)
 41. The method as in claim 36, wherein: the secondsemiconductor substrate includes a silicon substrate or aninsulator-on-silicon substrate that is fabricated with circuitry priorto the transfer of the fabricated photoelectronic semiconductorstructures; and the method further includes coupling the circuitry tothe fabricated photoelectronic semiconductor structures to form a deviceon the second substrate.
 42. The method as in claim 36, wherein: thedevice formed on the second substrate includes: a photovoltaic moduleengaged to the new substrate and structured to convert light intoelectricity; a sensor module engaged to the new substrate and coupled toreceive power from the electricity generated by the photovoltaic module,the sensor module structured to include a sensing element that isresponsive to a target substance to produce a response, wherein thesensor module is configured to generate, based on the response from thesensing element, an electrical sensor signal indicative of a property ofthe target substance; and a light-emitting module engaged to the newsubstrate and coupled to receive power from the electricity generated bythe photovoltaic module and to receive the electrical sensor signal fromthe sensor module, the light-emitting module structured to produceoutput light that is modulated to carry the electrical sensor signal towirelessly and optically transmit the electrical sensor signal out ofthe device.
 43. (canceled)
 44. The method as in claim 36, comprising:performing a first etching process to remove the semiconductor substrateprior to performing the etching process to remove the semiconductorrelease layer.
 45. A method for sensing a target subject, comprising:implanting a sensor on a target subject without having a physicalconnection to the sensor; directing illumination light onto the sensorimplanted on the target subject to cause a photovoltaic module in thesensor to generate electric power for operating the sensor so that thegenerated electric power powers (1) a sensor module which performs asensing operation on the target subject to generate an electrical sensorsignal indicative of a property of the target subject, and (2) alight-emitting module coupled to receive the electrical sensor signalfrom the sensor module and operable to produce output light that ismodulated to carry the electrical sensor signal; and receive informationindicative of the property of the target subject by using the outputlight to wirelessly and optically transmit the electrical sensor signalout of the device.
 46. The method as in claim 45, comprising: directingan optical communication signal to the sensor to wirelessly andoptically send information associated with an operation of the sensorvia the optical communication signal to the sensor.
 47. The method as inclaim 46, wherein: an optical wavelength of the optical communicationsignal is different from an optical wavelength of the illuminationlight. 48-53. (canceled)
 54. A device with opto-electronic circuitry,comprising: a substrate; a photovoltaic module engaged to the substrateand structured to convert light into electricity; a sensor moduleengaged to the substrate and coupled to receive power from theelectricity generated by the photovoltaic module, the sensor modulestructured to include a sensing element that is responsive to a targetsubstance to produce a response, wherein the sensor module is furtherconfigured to generate, based on the response from the sensing element,an electrical sensor signal indicative of a property of the targetsubstance; and a light-emitting module engaged to the substrate andcoupled to the photovoltaic module and the sensor module throughelectrical one or more interconnects having a dimension less than 10microns to receive power from the electricity generated by thephotovoltaic module and to receive the electrical sensor signal from thesensor module, the light-emitting module structured to produce outputlight that is modulated to carry the electrical sensor signal towirelessly and optically transmit the electrical sensor signal out ofthe device.
 55. The device as in claim 54, wherein: the sensor module isstructured to generate the electrical sensor signal indicative of atemperature of the target substance, a presence of a biological orchemical substance in the target substance, or an electrical property ofthe target substance. 56-61. (canceled)